Here's my 2¢...
I've tried it because 1) I've been curious why some people enjoyed it and 2) I have BPH and wanted to know if it would help improve my urine stream and allow me to ditch the stupid-expensive Rx with the bummer side-effects. So, I studied up on anatomy, found a medical clip on YouTube, studied up on sterile procedure, and purchased a shelf-full of supplies, e.g, sterile gloves, sterile lube, "sterile field" pads, etc, etc, and I figured out how to successfully insert sterilized Van Buren dilators past my prostate without injury and the results were...
1) Well blow me down, as long as I didn't have an active infection, it really did feel fantastic. Amazing. No wonder. Wow!
2) My urine stream improved dramatically. I mean like, "Yes! This is great! Peeing feels good again!"
3) No matter what well-thought out, carefully followed steps I took, after 2 or 3 sessions I would inevitably come down with a f***ing infection that would send me to my urologist. After 3 rounds of that game, I gave up.
My advice...
Try it if you must, but even if you manage not to injure yourself, it's probably only a matter of time before you come down with an infection.
However, as long as you never go past about 4", keep everything as sterile as you can, and make sure to pee afterwards, you'll probably not have a problem.